The present invention relates to a high performance planing hull, in terms of speed and carrying load, provided with a trim tab system. The term “trim tab” is intended as a surface and/or volume positioned at the immersed part of the stern, capable of adjusting the hull trim with respect to the free surface of the water in specific operating conditions.
The prior art comprises planing hulls provided with movable surfaces used to adjust the trim of the boat, known as trim tabs or flaps. When these surfaces are struck by a water flow they generate a hydrodynamic force, which is multiplied by the existing arm between the point in which force is applied and the centre of gravity of the hull to determine a couple that modifies the trim of the boat with respect to the surface of the water.
The couple generated determines rotation of the hull about the pitch axis of the boat.
The surface of the trim tab can be provided with actuating means which allow relative movement thereof with respect to the water flow which strikes it, allowing the user of the boat to “adjust” the amount of trim adjusting couple when there is a variation of speed and conditions of use.
In the case of movable trim tabs, the prior art describes many systems to produce movement of the surface with respect to the water flow which strikes it. In some systems, the actuating means allow simple translation of the movable surface in one direction, while in other more complex systems they allow rotation with respect to an axis.
Prior art hulls are provided with a pair of movable trim tabs installed in lateral position with respect to the propulsion system of the boat, so as not to influence, or be influenced by, the water flow generated.
Various actuating systems, generally of pneumatic or hydraulic type, can be adopted for movement of the surfaces by the user of the boat.
The actuating means of the trim adjusting systems formed by movable surfaces have the considerable drawback of being installed in areas subject to high levels of humidity and salinity, if the hull is used in sea water. These phenomena are particularly hazardous for mechanical parts, which require frequent maintenance.
EP-0794115 describes a planing hull designed to allow housing of the actuating means of the two movable lateral surfaces and prevent contact with water or with atmospheric agents from causing problems of corrosion and making frequent maintenance operations necessary.
The recent increase in the use of high performance planing hulls, in terms of speed and useful carrying load has led to further problems concerning the trim of the boat in some conditions of use and in particular during acceleration before reaching a stable planing trim.
For reasons of dynamic stability, high performance planing hulls are designed so that the centre of gravity is positioned relatively far back with respect to the total length of the hull. In fact, in high performance hulls, the position of the centre of gravity is located at a distance from the stern of 25-40% of the length of the hull.
Although allowing high performance in terms of speed, this characteristic leads to “bow up” trim during acceleration, i.e. the bow of the boat is lifted high above the surface of the water, with consequent visibility problems.
Moreover, in standing start, manoeuvring and/or low speed operating conditions the hydrodynamic force acting on the hull is null or of negligible intensity.
When the navigation speed increases and the hull is planing, conditions of visibility and trim improve considerably, causing “bow down” and allowing navigation in safe conditions.